For example, an AE (Acoustic Emission) sensor is a sensor that senses vibrations in the acoustic band and the ultrasonic band. AE is, for example, an elastic wave in the ultrasonic band occurring due to the occurrence and/or propagation of a crack. For example, the AE sensor is used in the sensed fatigue/degradation diagnosis, non-destructive testing, etc. It is desirable to the increase of the sensitivity of the sensor.